At Harpers Ferry, Captain Meriwether Lewis obtained 15 rifles built
under contract for the United States Army in 1792 and 1794. Gunsmiths
from Lancaster County, Pennsylvania, produced these rifles. According
to the records in Lancaster, these were .49 caliber weapons, with a
42-inch barrel that featured a patch-box with a push-button release.
Over 300 of these rifles were stored at the Harpers Ferry arsenal when
Lewis arrived in April 1803.

From the 18 May 1803 requisition receipt Lewis received from the arsenal,
the 25 May 1803 letter from Secretary of War Henry Dearborn to the Superintendent
of the Harpers Ferry Arsenal Joseph Perkin, and the 8 July 1803 letter
from Lewis to Jefferson, it appears that Lewis had the arsenal shorten
the barrels of 15 of the 1792 / 1794 rifles to between 33 and 36 inches
and re-bored. He also had the gunsmiths add swivels to these weapons,
and fit them with new locks. Additionally, Lewis purchased replacement
locks and spare lock parts for each rifle.

Significantly, the requisition paperwork from Harpers Ferry does not
mention the specific type of weapon Lewis obtained. This is certainly
not consistent with Army regulations, unless the arsenal had only one
type of weapon in stock, in which case it was not necessary to specify
the type procured. This leads to the conclusion that the arsenal had
only one rifle in stock – the 1792 / 1794 model. Moreover, Dearborn's
letter to Perkin supports this, especially when Dearborn states that
he prefers the short rifle Lewis had shown him "over the long ones
(commonly used) in actual service". From reading Dearborn's letter,
it becomes clear that the Secretary of War was convinced that the Army
needed rifles like the one Lewis had procured for the expedition, and
Dearborn orders Perkin to begin manufacturing "a suitable number."

From the available evidence, it seems that Dearborn was so impressed
with the short rifles Lewis had the armory make for the expedition that
he ordered Perkin to produce similar ones for the entire Army. In fact,
Dearborn's letter specifies in great detail the type of rifle the armory
is to manufacture. But it wasn't until October 1803 that the first of
these 1803 rifles was finished. By that time, Lewis and Clark were leaving
the Falls of the Ohio River, near Louisville, Kentucky.

Some believe that the contract rifles Lewis had modified for the expedition
were the prototype for the M1803 rifle. While this may be true, the
available evidence demonstrates that the expedition members carried
modified 1792 / 1794 rifles, not the M1803 ones.